This invention pertains to magnetic recording media.
FIG. 1 illustrates a typical prior art magnetic recording medium 1 comprising a substrate 2 (e.g. an aluminum alloy 2a plated with a NiP alloy 2b), a Cr (or Cr alloy) underlayer 4, a magnetic Co alloy layer 5, and a protective overcoat 6. NiP alloy layer 2b is textured prior to deposition of layers 4, 5 and 6. Cr underlayer 4 has a bcc crystal structure and a (200) crystal orientation. Underlayer 4 ensures that hcp Co alloy layer 5 nucleates and grows with 1 1 2 0 crystal orientation. Further, Cr underlayer 4 also ensures that magnetic Co alloy layer 5 exhibits magnetic anisotropy in the direction of texture lines formed in layer 3.
Instead of using a single Cr underlayer 4, it is known to form a recording medium 1a comprising first and second Cr underlayers 4a, 4b (FIG. 2). See, for example, U.S. Pat. No. 6,303,217, issued to Malhotra et al., which discusses a structure in which layer 4a is Cr, and layer 4b is a CrMo20 alloy. (As used herein, a reference to an alloy CrAx refers to a composition Cr100-xAx. Similarly, CrAxBy refers to a composition Cr100-x-yAxBy.) Pure Cr is more compatible with NiP layer 2b than the CrMo20 layer 4b, and CrMo20 provides a better nucleating surface for the Co alloy than pure Cr. Thus, medium 1a of FIG. 2 exhibits better performance than medium 1 of FIG. 1. (Malhotra reports that medium 1a exhibits improved noise performance.)